The invention relates to electronic circuits which include magnetic devices and, in particular, to a method for automatic in-line assembly of circuits including such devices.
Electronic circuits including magnetic devices such as inductors and transformers serve a wide variety of essential functions. Such circuits, for example, serve as power supplies. Inductors are used as choke coils for energy storage and to minimize noise and AC ripple, and transformers are used to change voltage level and provide isolation. The magnetic devices are often made of a magnetic core, such as ferrite, wound with conductive coils.
Magnetic devices have historically been difficult to miniaturize. The profile heights of magnetic devices have been reduced through the use of ferrites. See U.S. Pat. No. 5,574,420 issued to A. Roy et al. on Nov. 12, 1996 and U.S. Pat. No. 6,094,123 issued to A. Roy on Jul. 25, 2000, which are incorporated herein by reference. However even these devices must be assembled as essentially complete units (coils wound around ferrites) before being applied in hybrid circuits.
A more recently developed approach to assembling magnetic devices on a substrate such as PC board is to print a conductive coil on the board around an aperture and bond together two parts of a ferrite body extending through the aperture.
To make a high quality device, the bond must be thin, uniform in thickness and durable. As a consequence, it has been necessary to clamp the ferrite parts together under pressure while the adhesive cures. This clamping step is time-consuming and typically requires manual intervention, thereby precluding automatic in-line assembly. Accordingly there is a need for a fully automatic process for the assembly of circuits containing magnetic components.
In accordance with the invention, an electronic circuit containing one or more magnetic devices is assembled by the steps of providing a substrate including an aperture and conductive coil extending peripherally around the aperture and bonding together two parts of a magnetic body extending through the aperture. The two parts have substantially planar mating surfaces, and the bonding is effected by securing one of the parts to the substrate, applying adhesive to the portion of its mating surface exposed within the aperture, and pressing the mating surface of the second part into contact with the mating surface of the first part. During pressing, the mating surfaces are rotated in a reciprocating fashion to spread the adhesive into a thin, highly uniform film. This process permits the formation in the cure operation of a high quality bond without clamping. It thus produces a high quality magnetic device without manual intervention and can be part of a fully automated process to fabricate a circuit assembly. In a preferred embodiment, the substrate includes auxiliary apertures for receiving corresponding protrusions from a part in the form of an E core and the mating surface of the E core extends through the coil aperture where it is bonded to a part in the form of a flat core.